At a glance: choosing an automatic transfer switch
- An automatic transfer switch (ATS) can switch from mains electricity to a compatible backup generator when it detects a power failure.
- Compatibility comes first. Not every generator supports ATS, even if it has electric or remote start.
- Look for a dedicated ATS input and check that the transfer switch is approved for the specific generator you're using.
- Size your generator for the equipment you need to keep running. An ATS doesn't increase the amount of power your generator can provide.
- Check whether your setup is single-phase or three-phase, along with the voltage and current requirements of the installation.
- Petrol generators can support automatic backup when they're ATS-compatible, so an ATS setup doesn't automatically mean choosing diesel.
- Use a suitably qualified electrician for installation where the transfer switch forms part of your mains electrical setup.
If you’re looking for an automatic transfer switch, the first thing to check is whether it will actually work with your generator.
An ATS isn’t a universal accessory. The generator needs the correct connection and the transfer equipment needs to suit the generator, your electrical supply and the load you want to keep powered.
You also need enough generator output for that load. Get compatibility and generator size right first and you’ll have a much clearer starting point for choosing your backup setup.
What does an automatic transfer switch do?
An automatic transfer switch forms part of a backup-power setup.
With a compatible system, it can detect a loss of mains power and trigger the change to generator power automatically. When the mains supply returns, the system can transfer the load back again.
That can be useful if you want important equipment to keep running without someone being there to manage the changeover manually.
The ATS itself doesn’t generate any electricity. Your generator still needs enough output to power the equipment connected to the backup system.
What should you look for when buying an automatic transfer switch?
Before comparing individual switches, check the basics of your setup.
You'll need to know:
- Which generator you'll be using
- Whether that generator has a compatible ATS input
- Whether you have a single-phase or three-phase supply
- The voltage and current requirements
- What equipment needs backup power
- How much generator output that equipment requires
- Where and how the system will be installed
Don’t assume that two products described as “ATS compatible” will automatically work together. Check the requirements for the exact generator and transfer switch before you buy.
How do you know if your generator is ATS-compatible?
Start with the generator specification. You're looking for a dedicated ATS input and confirmation that the model supports automatic transfer.
Electric start on its own isn't enough. A generator may be capable of starting at the turn of a key without having the connection needed for an ATS to start it automatically.
Remote start can cause similar confusion. Some generators support remote starting but not ATS. One current wireless-start diesel model, for example, specifically states that ATS isn't supported, while the electric-start version of the same 6.25 kVA generator does include an ATS input.
So check the individual model rather than making a decision based on its starting method.
Can you use an automatic transfer switch with a petrol generator?
Yes. Automatic backup isn't limited to diesel generators.
Compatible petrol generators can include an ATS input, allowing them to form part of an automatic backup-power setup.
For home backup and other relatively occasional power requirements, that means petrol may be worth considering before moving straight to a larger diesel setup.
Think about how often you're likely to use the generator, how much power you need and whether portability matters alongside the automatic backup function.
What about a dual-fuel generator?
A dual-fuel generator can be useful if you'd like the option of running on petrol or LPG.
That fuel flexibility is separate from ATS compatibility, though. A generator being dual-fuel doesn't automatically mean it can work with an automatic transfer switch.
If you want both features, check the individual generator specification for ATS compatibility and make sure its output on your chosen fuel is sufficient for your backup-power requirements. Output can differ between petrol and LPG on some dual-fuel generators.
When should you consider a diesel generator with ATS?
A diesel generator may make more sense when your backup requirements involve heavier loads or longer periods of use.
ATS-compatible diesel generators are available for standby and backup applications across a range of outputs.
That doesn’t mean you need diesel simply because you want automatic changeover. For lighter or occasional backup requirements, an ATS-compatible petrol generator may provide the power you need.
Look at the workload first. Then compare the fuel types and generators capable of handling it.
What size generator do you need for an ATS setup?
This is one of the most important parts of the buying decision.
An automatic transfer switch doesn't give your generator any additional power. If you want to keep certain appliances or equipment running during an outage, the generator needs enough rated output to support them.
Start by deciding what's genuinely essential. You may want backup for heating, refrigeration, alarms and a selection of other equipment rather than trying to power everything normally connected to the property.
Then calculate the combined running requirements and account for any equipment with a higher starting demand.
Correct sizing is especially important with an automatic setup because the system needs to work as intended when you're not there to make decisions about which equipment gets switched on.
Do you need single-phase or three-phase ATS?
The answer depends on your electrical supply and the generator you're using.
Many homes use a single-phase supply, while three-phase electricity is more commonly found where larger electrical loads or commercial equipment are involved.
Some ATS panels can work with both types of supply; our diesel ATS, for example, supports 220–415V and both single- and three-phase applications when paired with a compatible generator.
Don't choose between single-phase and three-phase based on the generator alone. The ATS needs to suit the electrical installation as a whole.
If you're unsure what supply you have or what the installation requires, this is something to establish with your electrician before ordering equipment.
Automatic vs manual transfer switch: which should you buy?
The choice comes down to how you want your backup power to operate.
An automatic transfer switch monitors the mains supply and can manage the change to generator power automatically with a compatible setup.
A manual transfer switch requires someone to carry out the changeover.
Automatic transfer is useful when you want backup power available even if nobody is there to start the generator and manage the changeover. A manual system may be enough where outages are infrequent and you're happy to manage the process yourself and perhaps turn off non-essential appliances first.
If you're still deciding whether automatic transfer is necessary, we've covered how ATS systems work separately.
Who should install an automatic transfer switch?
An ATS connected between your mains supply and backup generator becomes part of your electrical setup, so correct installation is vitally important.
While the connection between a compatible ATS and generator may be designed to be straightforward, that doesn't make installation at the mains or consumer-unit side a DIY job.
Use a suitably qualified electrician to assess and install the system. They can confirm the electrical requirements, changeover arrangement and whether the generator and transfer switch are appropriate for the installation.
You should also check the generator manufacturer's requirements before fitting third-party transfer equipment. Using an unsuitable transfer system can affect warranty coverage on some generators.
Automatic transfer switch buying checklist
Before buying an ATS, make sure you can answer these questions:
- Does my generator support ATS?
- Is this transfer switch compatible with my specific generator?
- Does the generator have the required ATS input?
- Is my electricity supply single-phase or three-phase?
- What equipment needs backup power?
- Is my generator large enough for that electrical load?
- Are there any significant starting-power requirements?
- Does the ATS meet the voltage and current requirements of my setup?
- Who will install the system?
- Have I checked the generator manufacturer's compatibility and warranty requirements?
If you're buying the generator and ATS together, check these points as part of the same decision rather than choosing the generator first and trying to add automatic transfer later.
Need help choosing a compatible ATS setup?
The most important thing is making sure your generator, automatic transfer switch and electrical requirements work together.
If you're unsure about compatibility or which generator you'll need for your backup setup, use our chat system to help you narrow down the right equipment before you buy.
